1. Field of the Invention
The present invention generally relates to computer-implemented methods, carrier media, and systems for stabilizing output acquired by an inspection system. Certain embodiments relate to a computer-implemented method for stabilizing output acquired by an inspection system by stabilizing output acquired for a wafer by the inspection system to a reference characteristic.
2. Description of the Related Art
The following description and examples are not admitted to be prior art by virtue of their inclusion in this section.
Fabricating semiconductor devices such as logic and memory devices typically includes processing a substrate such as a semiconductor wafer using a large number of semiconductor fabrication processes to form various features and multiple levels of the semiconductor devices. For example, lithography is a semiconductor fabrication process that involves transferring a pattern from a reticle to a resist arranged on a semiconductor wafer. Additional examples of semiconductor fabrication processes include, but are not limited to, chemical-mechanical polishing (CMP), etch, deposition, and ion implantation. Multiple semiconductor devices may be fabricated in an arrangement on a single semiconductor wafer and then separated into individual semiconductor devices.
Inspection processes are used at various steps during a semiconductor manufacturing process to detect defects on wafers to promote higher yield in the manufacturing process and thus higher profits. Inspection has always been an important part of fabricating semiconductor devices such as integrated circuits (ICs). However, as the dimensions of semiconductor devices decrease, inspection becomes even more important to the successful manufacture of acceptable semiconductor devices because smaller defects can cause the devices to fail. For instance, as the dimensions of semiconductor devices decrease, detection of defects of decreasing size has become necessary since even relatively small defects may cause unwanted aberrations in the semiconductor devices.
In order for inspection to provide useful results for yield control, the inspection process must be able to discriminate between real defects on the wafer and noise or nuisance events. Noise may be generally defined as events detected on a wafer by an inspection tool that are not actually defects but appear as potential defects due to marginalities in the inspection tool such as marginalities in data processing and/or data acquisition. Nuisance events are actual defects but are not relevant to controlling the process or predicting yield. In some instances, the noise and nuisance events detected by an inspection tool can be reduced by using optimized data acquisition parameters and optimized data processing parameters. In addition, the noise and nuisance events can be reduced by applying various filtering techniques to the inspection results.
As design rules shrink, however, semiconductor manufacturing processes may be operating closer to the limitations on the performance capability of the processes. In addition, smaller defects can have an impact on the electrical characteristics of the device as the design rules shrink, which drives more sensitive inspections. Therefore, as design rules shrink, the signals corresponding to defects detected by inspection systems may be lower, while the noise detected by the inspection systems may be much higher due to the limitations in the processes. As such, discriminating between defects and noise is becoming much more difficult. Unless such issues are addressed adequately, the accuracy of defect detection and therefore the ability to monitor and control semiconductor fabrication processes may be dramatically reduced.
Furthermore, variations in the process itself may cause variations on wafers (from wafer-to-wafer and within wafer) that may appear as noise and/or nuisance events in the output acquired for the wafers by an inspection system. For example, an inspection recipe used for a particular layer of a wafer is typically setup using one wafer, and then the inspection recipe is re-used for the same layer on other wafers. However, if the additional wafers vary from the wafer used to setup the recipe due to process variations, the variations may appear as noise and/or nuisance events in the output acquired for those wafers by the inspection system. Such noise and/or nuisance events can be so overwhelming as to make real defects and/or defects of interest (DOI) impossible to detect using the output acquired by the inspection system. Therefore, such process variations can cause an inspection recipe to be unstable over time, possibly to the extent that the recipe must be changed or even a new recipe created such that wafers subject to the process variations can be inspected. In addition, typically such variations are not interesting to the user of the inspection system. As such, output of an inspection system responsive to such process variations can not only make defect detection difficult if not impossible but there is also no advantage to detecting such process variations.
Accordingly, it would be advantageous to develop computer-implemented methods, carrier media, and systems for stabilizing output acquired by an inspection system using an inspection recipe.